1. Field of Invention
The present invention relates generally to an electronic device and a method for controlling a charging operation of a battery.
2. Description of Related Art
In general, methods of charging batteries include a method of charging a battery at a Constant Current (CC), a method of charging a battery at a Constant Voltage (CV), and a method of charging a battery at a Constant Power (CP). In addition, methods of charging batteries include a Constant Current-Constant Voltage (CC-CV) charging method of charging a battery by combining a constant current charging method and a constant voltage charging method, a multistage current charging method of charging a battery after varying the intensity of the constant current, and a boost (CV-CC-CV) charging method in which current larger than the Constant Voltage and the CC-CV charging method are combined with a constant voltage charging method.
FIG. 1 is a graph depicting a general relationship between voltage and electric charge as battery charging time passes.
Referring to FIG. 1, it can be seen that a maximum battery allowable current 110 decreases and an opened circuit voltage 120 increases as the battery is charged. When the battery is charged at a constant voltage, the battery may be automatically charged at a maximum allowable battery current. In this way, if the battery is charged at the maximum allowable battery current, the charging speed becomes faster. However, if the battery is charged at a high rate, the temperature of the battery rapidly increases due to a resistance component in the battery.
FIG. 2A is a graph depicting a change in the temperature of a battery according to the charging time corresponding to a maximum temperature in a multistage current charging section, according to the related art. FIG. 2B is a graph depicting a change in temperature of a battery according to a charging time corresponding to a maximum temperature in a constant voltage section, according to the related art.
Referring to FIG. 2A, a temperature rise occurs most significantly in a multistage current charging method, according to the related art, such that a temperature rise is unbalanced and the temperature of the battery decreases heavily when a constant voltage charging operation starts. Because current decreases in step form due to an unbalanced result caused by an asymmetric temperature, the temperature generated by a resistance component of the battery is significantly reduced as compared with a temperature generated by a change in entropy of the battery and a temperature transferred to the surrounding area such that the temperature rise is small and the maximum temperature point is generated in a multistage current charging section. However, in the case of an initial charging speed, because an average value of a charging current decreased in steps is smaller than a charging current decreased continuously, a charging time for the charging amount becomes longer than that illustrated in FIG. 2B.
Referring to FIG. 2B, because a temperature rise occurs most significantly in a constant voltage charging operation, an imbalance may be generated and a charging time may be reduced. Because a charging current becomes continuously smaller without being reduced in steps at an initial stage if an unbalance is generated, a temperature rise due to a resistance component of the battery becomes larger than that illustrated in FIG. 2A and a maximum temperature point is generated in a constant voltage section. However, an initial charging speed may be faster than that illustrated in FIG. 2A because an average charging current value is large.
In these conventional charging methods the temperature of the battery rises when the battery is charged in a multistage current charging section and a constant voltage section.
However, because increased temperatures which result when the battery is charged are rarely considered in the conventional charging methods, the temperature of the battery may rise significantly if the battery is charged at a high speed. The temperature rise may, as a result, affect peripheral devices.
Further, the internal temperature of the battery is far higher than the surface temperature of the battery. As a result, if the surface temperature of the battery is slightly increased, the internal temperature of the battery is significantly increased and, the life span of the battery abruptly decreases as the internal temperature rises.
Accordingly, it is necessary to optimize the temperature generated while the battery is charged.